The present invention relates to a video signal processing circuit, and more particularly to a processing circuit to make an aperture correction or a picture quality restoration of a digitalized video signal in a video tape recorder (VTR) etc.
Television cameras pick up pictures and cathode ray tubes produce pictures by scanning electron beam. Since the section of such an electron beam is definite in size sudden changes of brightness or highly contrastd edges of pictorial images result in so-called "blurring" in the images. To correct such a blurring, aperture correction to compensate for degradation of higher frequency band components has been conventionally made.
Since the luminance signal band in home VTRs etc. is narrower than the corresponding broadcasted signal band, the image enhancement is conducted for the purpose of increasing the sharpness of the pictorial images.
A conventional aperture correction circuit is of the type using a single or two delay lines. The problem with such an aperture correction circuit is as follows. First, ringing or smear is likely to occur. Particularly, when correction is implemented to a color difference signal or a component signal, color ringing occurs. Especially in case where a noise is superimposed on an input signal, degradation of S/N ratio of the signal is inevitable.
In addition, the high frequency range of the frequency characteristic is solely emphasized in the above-mentioned respective conventional circuits, resulting in the problem that the noise components of the high frequency range are increased. To eliminate this problem, a circuit has been proposed in which a noise suppression circuit to suppress noise components is provided in such circuits.
However, the problem inherent to the last-mentioned circuit is that it is difficult to set the noise suppression level in the noise suppression circuit.